Being possessive of Victor likely flipped his switch
No, really, here’s why:
Before the competition, Yuri has to keep hearing people tell him to not monopolize Victor, and hear people telling Victor to leave him:
It made him come to the realization that no one would be satisfied with him having Victor -thus removing him from the competition- if they thought he was unworthy.
And that flipped his switch. Yuri wanted it to be clear to other that Victor was his alone, and he wasn’t just anyone, but someone important to Victor, and that he was worthy of that.
This performance wasn’t just about seducing Victor but also about flaunting his conquest, and his importance, to others.